Degradation and impact of phthalate plasticizers on soil microbial communities

To assess the impact of phthalates on soil microorganisms and to supplement the environmental risk assessment for these xenobiotics, soil was treated with diethyl phthalate (DEP) or di (2-ethyl hexyl) phthalate (DEHP) at 0.1 to 100 mg/g. Bioavailability and membrane disruption were proposed as the c haracteristics responsible for the observed fate and toxicity of both compo unds. Diethyl phthalate was biodegraded rapidly in soil with a half-life (t (50)deg) of 0.75 d at 20 degrees C, and was not expected to persist in the environment. The DEHP, although biodegradable in aqueous solution (t(50)deg < 15 d at 20 degrees C), was recalcitrant in soil, because of poor bioavai lability (only 10% degraded by 70 d at 20 degrees C) and was predicted to a ccount for the majority of phthalate contamination in the environment. Addi tion of DEP or DEHP to soil at a concentration similar to that detected in nonindustrial environments (0.1 mg/g) had no impact on the structural diver sity (bacterial numbers, fatty acid methyl ester analysis) or functional di versity (BIOLOG) of the microbial community. At concentrations representati ve of a phthalate spill, DEP (>1 mg/g) reduced numbers of both total cultur able bacteria (by 47%) and pseudomonads (by 62%) within 1 d. This was due t o disruption of membrane fluidity by the lipophilic phthalate, a mechanism not previously attributed to phthalates. However, DEHP had no effect on the microbial community or membrane fluidity, even at 100 mg/g, and was predic ted to have no impact on microbial communities in the environment.